Control for an electromagnetic brake for a multiple-ratio power transmission that has a brake actuation counter

ABSTRACT

A control system and method for an electromagnetic clutch brake, including an electromagnetic clutch brake actuator coil surrounding a power input shaft for a multiple-ratio transmission in a vehicle powertrain. A protective circuit of the control system normally monitors data inputs from a databus that may indicate conditions that are not favorable for clutch brake actuation. The protective circuit prevents actuation of the clutch brake under such conditions. In the event the data inputs are not available from the databus, the protective circuit permits operation in a fall-back mode in which a brake ON timer is checked prior to clutch brake actuation. A primary counter is incremented with each normal clutch brake actuation and a secondary counter is incremented with each fall-back clutch brake actuation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.11/369,245, filed Mar. 7, 2006, now U.S. Pat. No. 7,597,651, issued Oct.6, 2009 which is a continuation-in-part of U.S. application Ser. No.11/143,069, filed Jun. 2, 2005, now U.S. Pat. No. 7,318,515, issued Jan.15, 2008 entitled “Electromagnetic Brake for a Multiple-Ratio PowerTransmission in a Vehicle Powertrain,” which is a continuation-in-partof U.S. application Ser. No. 10/760,665, filed Jan. 20, 2004, now U.S.Pat. No. 7,000,748, dated Feb. 21, 2006 entitled “Clutch Brake.”

BACKGROUND OF THE INVENTION

1. Field of the Invention

A protection circuit and controller for an electromagnetic frictionbrake for a heavy-duty power transmission for controlling decelerationof a torque input shaft for the transmission during transmission ratiochanges.

2. Background Art

A powertrain for a heavy-duty vehicle, such as a truck or a tractortrailer, typically has an engine that is connected by a master clutch,under the control of the vehicle driver, to a power input shaft for amultiple-ratio geared transmission. Driver operated shift rails andshift forks can be used to establish and interrupt torque flow pathsthrough selected gear elements of the multiple-ratio transmission. Ratiochanges can be accomplished manually by shifting synchronizer clutchsleeves into and out of engagement with companion gear elements or byshifting non-synchronized gear or clutch elements. The gear elements mayform a driving torque flow path through a transmission main shaft and acountershaft to a torque output shaft.

Multiple-ratio transmissions of this type, as well as heavy-duty powertransmission mechanisms with power actuated clutches for establishingand interrupting torque flow paths through the gearing, are well known.A ratio changing shift sequence typically involves disengagement of themaster clutch to interrupt power flow from the vehicle engine to thetorque input shaft of the transmission as the transmission clutchelements are selectively engaged and disengaged. When the master clutchis disengaged, a torque input shaft for the transmission must decelerateso that the gear elements of the on-coming torque flow path aregenerally synchronized.

A brake may be used to facilitate shifting of the transmission gearingby decelerating the transmission torque input shaft thereby decreasingthe time required to accomplish a ratio shift. A torque input shaftbrake is especially useful when the vehicle driver initiates a shiftfrom neutral to low ratio or from neutral to reverse after disengagingthe master clutch.

It is known in the art to provide a transmission input shaft brake thatincludes a friction member connected in a driving relationship, such asby splines, to the transmission torque input shaft. The transmissionmaster clutch is disengaged by a master clutch release mechanism so thatwhen the master clutch is disengaged, the release mechanism may apply abrake engaging force on the transmission input shaft brake. Frictionbrake elements of the input shaft brake are frictionally engaged tocreate a frictional drag torque that decelerates the transmission inputshaft.

Co-pending patent application Ser. No. 10/760,665, filed Jan. 20, 2004,now U.S. Pat. No. 7,000,748, issued Feb. 21, 2006, discloses atransmission input shaft brake with an electromagnetic brake actuator.That co-pending application is assigned to the assignee of the presentinvention. The electromagnetic brake disclosed in the co-pendingapplication comprises an armature that is secured to the transmissioninput shaft adjacent a friction surface formed on an adjacenttransmission housing wall. When the brake is energized, the armature isfrictionally engaged with a stationary friction surface on thetransmission housing wall thereby retarding or preventing rotation ofthe transmission torque input shaft at the outset of a ratio shift.

The electromagnetic brake of the co-pending application creates amagnetic flux flow path that is defined in part by a brake armature. Theflux flow path envelopes portions of the transmission, including thetransmission input shaft, a transmission input shaft bearing and bearingcover, and portions of the driver operated master clutch releasemechanism.

The electromagnetic input shaft brake disclosed in the co-pendingapplication includes a housing, which may replace a transmission inputshaft bearing cap typically found on heavy-duty transmissions. Theelectromagnetic brake includes coil windings that are placed close tothe input shaft to reduce the length of the coil windings and to reducethe amount of copper required in the manufacture of the coil. Typically,the electromagnetic brake is strategically positioned to minimize thespace required to accommodate it in the transmission assembly.

The magnetic lines of flux created as the transmission input shaft brakeis activated pass through the transmission input shaft and surroundingportions of the transmission that are of high carbon content, which maybe magnetized following a period in which the transmission input shaftbrake is frequently activated. It is possible, for example, for thetransmission input shaft to be partially magnetized with a residualmagnetic intensity that can remain even after the brake is de-energized.The transmission housing, which typically is formed of cast aluminum orcast iron with a low carbon content, does not readily become magnetizedbecause those materials are relatively poor conductors for magnetic fluxfields. The input shaft itself, however, as well as the bearing elementsand other transmission elements and seal covers, are formed of highcarbon steel and are in close proximity to the input shaft brake.

The return flux flow path in an arrangement of this type typicallyincludes an armature plate of the input shaft brake, which may be asolid disk design because of its ease of manufacture and its low cost.

Because of partial or residual magnetization of transmission componentsin proximity to the input shaft brake, ferrous particles in an operatingenvironment for the transmission can be attracted to rotary portions ofthe transmission and damage transmission bearings, seals and othertransmission components.

An input shaft brake should not be engaged if the vehicle speed, idlespeed, or when an operator is depressing the accelerator pedal becausedamage could result to the clutch or transmission. The input shaft brakecontrol system may be difficult to program due to differences in engineset-up parameters required by different vehicle manufacturers.Differences in engine operating parameters and in different conditionsmake it difficult to always assure proper operation of the input shaftbrake in conjunction with the transmission.

The input shaft brake control system may be subject to thermal orelectrical overloading if there is excessive braking or if the currentdraw exceeds a safe limit. Thermal or electrical overloading of thecontrol system may adversely effect the control system and reducereliability of the system.

The electromagnetic brake may be connected to a databus that providesdata inputs that monitor conditions that may be appropriate orinappropriate for energizing the brake stator coil. When the protectioncircuit senses that it is not appropriate to energize the coil, thebrake is prevented from engaging. If the connection to the databus isinterrupted, the brake will be permitted to engage, but a counter willbe incremented to count unprotected brake engagements. A counter mayalso be used to count brake engagements while the protective circuit isoperational. The counts from the counters may be checked when the systemis serviced.

The above problems and others are addressed by applicants' invention assummarized below.

SUMMARY OF AN EMBODIMENT OF THE INVENTION

An electromagnetic brake and brake control system is provided for avehicle powertrain for a wheeled vehicle. The powertrain comprises anengine, a multiple-ratio power transmission having a housing enclosingmultiple-ratio gear elements, a power output shaft driveably connectedto vehicle traction wheels, a power input shaft driveably connected tothe multiple-ratio gear elements, and a master clutch selectivelyconnecting the power input shaft to the engine. The master clutch isenclosed by a master clutch housing forming a part of the transmissionhousing.

The electromagnetic brake comprises a stator coil housing secured to thetransmission housing, the stator coil housing encloses a stator coilthat surrounds the power input shaft and defining with the coil housingan electromagnetic pole face. An armature plate has a hub portionsecured to the power input shaft and a peripheral portion disposedadjacent the brake stator coil. A control system electrically energizesthe brake stator coil thereby effecting frictional engagement of thearmature plate with the pole face. An electromagnetic flux flow path isestablished around the coil through the stator coil housing and theperipheral armature plate portion.

The control system may include sensors for determining whether themaster clutch is disengaged, whether the transmission is in neutral,whether low transmission speed ratio is selected, whether reverse speedis selected, whether reverse speed is selected, whether the acceleratorpedal is depressed, and whether vehicle speed is less than apredetermined value, or other conditions. The above signals may beavailable from a vehicle datalink, such as a CAN based J1939 datalink.If the data from the datalink is unavailable, the electromagnetic brakewill continue to operate based upon an input signal from the clutchbrake activation switch. For example, the clutch brake activation switchmay be actuated when the clutch pedal is near or at the end of travelfor the clutch pedal.

A stator coil circuit includes a voltage source and a switch for openingand closing the coil circuit. A thermally responsive circuit protectormay be provided in the coil circuit for sensing the temperature of thestator coil whereby overheating of the stator coil is avoided. Thestator coil circuit may also include an overcurrent protector foropening the stator coil circuit when current in the stator coil exceedsa predetermined value.

A primary counter may be provided as part of the control system that isincremented upon each clutch brake activation under normalcircumstances, i.e., when the protection circuit based upon protectionlimits set by the control algorithm that are based on the datalinkinputs. Activation of the electromagnetic brake when the protectioncircuit is operational are considered normal actuations.

A secondary counter may be provided to count electromagnetic brakeactuations when the data signals are not available from the datalink andthe system is operating based upon an input signal from the clutch brakeactivation switch. Operation in this mode may be considered a harshoperation in which only limited protection is available for the brake.In such actuations, the brake may see excessive wear due to the brakebeing activated under conditions that would normally be prohibited bythe protection algorithm. The secondary counter keeps tracks ofengagements that occur while the protection circuit is disabled.

The primary counter increments upon each clutch brake activation whenthe protection circuit is operational. The secondary counter is activeif a datalink fault code is set upon detection of the loss of aconnection to the datalink. In the fall-back mode, each actuation of theelectromagnetic brake increments a secondary counter.

The primary counter and secondary counter may be inspected periodicallyto determine if the clutch brake has operated without the datalink basedprotection limits. If so, a service technician may determine how manyactivations occurred without the datalink protection limits. Theinformation from the counters may aid in diagnosis of wear and alsoprovide valuable information regarding usage of the electromagneticclutch brake and the extent of wear of the clutch brake.

These and other aspects of the invention will be apparent from thefollowing drawings and detailed description of an embodiment of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a prior art multiple-ratioheavy-duty power transmission mechanism that is capable of incorporatingthe present invention;

FIG. 2 is a partial cross-sectional view of a master clutch for thetransmission of FIG. 1 and an electromagnetic brake for the input shaftof the transmission;

FIG. 2 a is an enlarged partial cross-sectional view of anelectromagnetic brake for the input shaft, together with a portion ofthe transmission input shaft assembled with the electromagnetic inputshaft brake;

FIG. 3 is a cross-sectional view of the electromagnetic transmissioninput shaft brake illustrated in FIG. 2 a with the electromagnetic brakein the engaged state;

FIG. 3 a is a view corresponding to the view of the input brake in FIG.3 wherein the brake is in a disengaged state;

FIG. 4 is a schematic diagram of the electromagnetic brake of FIG. 2 awherein lines of flux of varying intensity are illustrated;

FIG. 5 is a partial cross-sectional view of a master clutch assembly,together with an electromagnetic brake for the input shaft of amultiple-ratio transmission in accordance with the teachings of thepresent invention;

FIG. 6 is a detailed plan view of an armature, which forms a part of theelectromagnetic input shaft brake of FIG. 5;

FIG. 6 a is a modified armature design corresponding to the design ofFIG. 6 wherein the friction member of the armature is formed in multiplesections;

FIG. 7 is a diagram illustrating the magnetic flux flow circuit for theelectromagnetic brake illustrated in FIG. 5;

FIG. 8 is a schematic controller diagram for the control of theelectromagnetic brake illustrated in FIG. 5;

FIG. 9 is a software flow diagram demonstrating the input shaftelectromagnetic brake control strategy for the electromagnetic brake ofFIG. 5;

FIG. 10 is an alternative embodiment of a software flow diagramdemonstrating the input shaft electromagnetic brake control strategy forthe electromagnetic brake of FIG. 5; and

FIG. 11 is a software flow diagram demonstrating the input shaftelectromagnetic brake control strategy wherein a primary counter and asecondary counter are provided to monitor brake actuation and wear indifferent modes of operation.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

FIG. 1 shows a known multiple-ratio heavy-duty truck transmissioncapable of embodying the electromagnetic input shaft brake of theinvention. The transmission of FIG. 1 is an example of a number oftransmissions that could incorporate the electromagnetic brake of theinvention. For example, multiple-ratio transmissions in automotivepowertrains with synchronizers for effecting synchronized engagement oftorque transmitting gear elements could be used. Other transmissionsthat could be used would include automated ratio shifting transmissionswith pneumatic or hydraulic shift actuators.

The transmission of FIG. 1 includes a clutch bell housing 10 and a maintransmission housing 12 that are secured together by bolts 14 to form atransmission housing assembly. The bell housing 10 can be bolted at 16to the engine flywheel housing of an internal combustion engine.

The transmission housing includes a forward bearing support wall 18 witha central bearing opening that receives and supports a main transmissionball bearing 20. A bearing cap 22 is secured to the wall 18. Atransmission input shaft 24 extends through the bearing cap and issupported by bearing 20. A lubrication oil seal 26 surrounds the inputshaft 24 and is retained by the bearing cap 22.

Torque input shaft 24 may be driveably connected to a torque input gear28 of the transmission mechanism. Gear 28 can be engaged driveably tocountershaft gears in known fashion. It may be connected also by a dogclutch 30 to a transmission main shaft 32 in known fashion. Torque inputshaft 24 is splined at 34 to establish a driving connection with aninternally splined friction clutch hub 36, as seen in FIG. 2.

The input shaft 24 of the known construction of FIG. 1 corresponds tothe input shaft 24′ of the construction of FIG. 2 a. Likewise, thesplined portion 34′ of the construction of FIG. 2 a corresponds to thesplined portion 34 of the known construction of FIG. 1.

The input shaft 24′ of FIG. 2 a is provided with an externally splinedportion 37, which registers with an internally splined gear element (notshown), which would correspond to torque input gear element 28 of theknown construction of FIG. 1. The torque input shaft 24′ is connected at38, such as by a spline or a key, to an armature ring 40, therebyestablishing a driving connection between torque input shaft 24′ andarmature plate 42. The ring 40 is connected to armature plate 42 byspring straps 44, which permit axial displacement of the plate 42 in thedirection of the axis of the shaft 24′. A small air gap 46 is providedbetween the armature plate 42 and an electromagnetic brake housing 48(sometimes referred to as a clutch-brake housing). The housing 48 issecured by bolts or other suitable fasteners 50 to a forward wall of thetransmission housing, which corresponds to the wall 18 seen in FIG. 1.

The housing 48 is provided with an annular pocket 52, which receiveselectromagnetic coil windings 54. An annular pole face is provided, asshown at 56. The face 56 is situated directly adjacent and injuxtaposition with respect to an annular face 58 of the armature plate42. When windings 54 are energized by an activating current, thearmature plate 42 is shifted into engagement with the friction face 46of the electromagnetic brake housing 48.

FIG. 3 shows the electromagnetic brake assembly of FIGS. 2 and 2 a whenthe coil windings are energized. At this time, the armature plate 42 isin frictional engagement with the friction surface 46 of the housing 48.The spring straps 44 flex, as shown in FIG. 3, as the armature plate 42is shifted toward the housing 48.

FIG. 3 a shows the position of the armature plate 42 when the coilwindings are de-energized. The residual spring force of the springstraps 44 move the armature plate 42 out of engagement with the surface46.

When the coil windings are energized, rotary motion of the input shaft24′ will be resisted by the frictional torque established by theelectromagnetic brake thereby decelerating the input shaft 24′.

FIG. 2 shows a master clutch construction for use in a transmissionhaving an input shaft corresponding to the shaft 24 of FIG. 1 or theshaft 24′ of FIG. 2 a. The spline portion 34′ of FIG. 2 a is driveablyengaged with the internally splined clutch hub 36. A damper spring cage60 is secured driveably to the hub 36, preferably by rivet elements 62.Damper springs 64 are received in the cage 60. The springs 64 engage aclutch drive plate 66 thereby establishing a resilient drivingconnection between the hub 36 and the clutch plate 66. Clutch frictionmaterials 68 and 72 are secured on both sides of the clutch plate 66.Friction material 68 is situated adjacent a friction surface 70 onengine flywheel 74. Friction material 72 is situated directly adjacentfriction surface 76 of clutch pressure plate 78, which is located withinrotary clutch housing 80, the latter being secured to the flywheel 74 sothat they rotate together. Pressure plate 78 is connected at itsperiphery to the clutch housing 80, the connection accommodating axialdisplacement of the pressure plate 78 relative to the clutch housing 80.

A diaphragm clutch actuator spring 82 is anchored at its periphery tothe clutch housing 80, as shown at 84. An intermediate portion of thediaphragm spring actuator 82 engages a pressure point on the pressureplate 78, as shown at 86. The radially inward margin 89 of the diaphragmspring 82 surrounds an inner bearing race 89 for clutch release bearingassembly 90. Axial displacement of the inner race 89 will cause axialshifting movement of the inner margin 89 of the diaphragm spring 82 as acollar 92 carried by the inner race 88 engages the periphery 89.

An outer race for the bearing 90 is an integral portion of clutchrelease bearing sleeve 94, which is provided with lubricating oilgrooves 96 extending in an axial direction, as indicated in FIG. 2. Thesleeve 94 is mounted about the axis of input shaft 24′, in knownfashion, between the electromagnetic brake housing 48 and the splineportion 34′. The clutch release mechanism includes a lever that ispivoted at 100 on the clutch bell housing. An arm 102 of the releaselever has an actuator end 104, as seen best in FIG. 2 a, which enters anannular space 106 seen in FIG. 2. The space 106 is defined by a ring 108secured to the sleeve 94 and by the release bearing 90.

The radially outward arm 110 of the release lever extends through thebell housing, shown at 10′, which corresponds to the bell housing 10 ofFIG. 1. A suitable actuator mechanism (not shown), which is under thecontrol of the vehicle operator and which is mechanically connected to atransmission clutch pedal, will rotate the clutch release lever toeffect shifting movement of the sleeve 94 in a left-hand directionagainst the opposing force of the diaphragm spring 82. The master clutchnormally is engaged under the spring force of the diaphragm spring 82.When the clutch release sleeve 94 is shifted in a left-hand direction asseen in FIG. 2, the clutch engaging force at 86 is released, and thepressure plate 78 is shifted out of engagement with the clutch plate 66.

FIG. 4 illustrates the flux flow path and magnetic field intensity forthe electromagnetic input shaft brake of FIGS. 2 and 2 a. The flux flowpath illustrated in FIG. 4 is identified by using magnetic finiteelement analysis software. FIG. 4 indicates that a magnetic flux fieldof maximum intensity at location 112 is in a flux flow circuit definedin part by the electromagnetic clutch-brake housing 48 and the armature42. The path envelopes in part the input shaft 24′, the region occupiedby the main transmission roller bearing assembly and the bell housing10′ itself.

The intensity of the magnetic flux field decreases as the field fluxflow lines separate from the vicinity of the electromagnetic brake coilwindings. Flux flow lines shown at 114 are of lower intensity, but theyenvelope several transmission elements that are formed of magneticmaterial, such as the diaphragm spring 82, the clutch housing and therelease bearing elements.

FIG. 5 shows the design of the present invention, wherein theelectromagnetic clutch housing is physically separated from the torqueinput shaft for the transmission. In the design of FIG. 5, the bearingcap does not form a part of the electromagnetic clutch-brake housing.The bearing cap is illustrated in FIG. 5 at 22′, which corresponds tothe bearing cap illustrated in the known design of FIG. 1. At a radiallyoutward location with respect to the bearing cap 22′ is anelectromagnetic clutch-brake housing 116.

The master clutch elements and the clutch release bearing of FIG. 5 maybe similar to the clutch and clutch release bearing illustrated in FIG.2. Reference numerals used in identifying the elements of the masterclutch assembly in the clutch release bearing in FIG. 5 are the same asthe corresponding elements of the FIG. 2 construction, although primenotations are added to numerals used in FIG. 5.

The electromagnetic clutch-brake housing 116 is provided with a pocket118, which receives electromagnetic coil windings 120. The diameter ofthe coil windings in FIG. 5 is larger than the diameter of the coilwindings shown in FIGS. 2, 2 a and 3. They are remotely situated withrespect to the transmission torque input shaft and the transmission mainball bearing. The clutch-brake housing 116 is bolted or otherwisesecured to bell housing 10′, although it could instead be secured totransmission housing wall 18. The bell housing 10′, for purposes of thisdescription, can be considered to be a part of the transmission housing.

A brake armature plate 122 is secured to the outer periphery of aflexible brake plate 124. The inner periphery of the brake plate 124 issecured to ring 126, which corresponds to the ring 40 shown in FIG. 2 a.

Details of the construction of the armature plate and the flexible plate124 are shown in FIG. 6. The flexible plate 124 comprises radiallyextending flexible arms 128. The outer margin of the flexible arms issecured to the armature plate 122. The inner periphery of the flexibleplate 124 is secured to armature ring 126.

FIG. 6 a shows an alternate construction in which the armature plate 122is formed in four separate segments 130. Although four segments areshown, it is possible to use a different number of segments if thatwould be preferred.

Unlike the design indicated in FIG. 2, where the armature plate freelyestablishes a flux flow path when the electromagnetic coil windings areenergized, the design of FIG. 6 and the design of FIG. 6 a provide arestricted flux flow path through flexible arms 128 in an inward radialdirection toward the transmission input shaft. To further isolatesurrounding elements of the transmission from the flux flow path, thearmature ring 126, which forms a hub for the armature, can be made ofnon-magnetic stainless steel.

FIG. 7 shows the path followed by the flux flow lines when the windingsat 120 are energized. The input shaft is not enveloped by the magneticflux flow lines, and the flux density illustrated in FIG. 7 isconcentrated in the electromagnetic brake where magnetic effects aredesired. The armature plate 122 or the armature plate segments 130establish a closed loop pattern as the flux flow lines are transferredfrom one electromagnetic pole to the other. The pattern for the fluxflow lines of FIG. 7 are distinct from the pattern illustrated in FIG.4, and the envelope for the flux flow lines is much more concentratedthereby avoiding undesired magnetization of the surrounding transmissionelements, the bearing elements, the torque input shaft, the sealelements and the clutch bell housing itself. The magnetic flux flow pathdoes not jump to adjoining components. With the design of FIG. 7, theopportunity for abrasive ferrous particles to gather and damage rotaryelements of the transmission, bearings and seals is substantiallyeliminated.

To further isolate the flux flow path, mounting fasteners for theelectromagnetic brake may be made of non-magnetic material such asaluminum or stainless steel, which isolates the flux conductors from thesurrounding components of the transmission and the master clutch.

The controller for the electromagnetic brake is schematicallyillustrated in FIG. 8, and a control algorithm for the electromagneticbrake is illustrated in FIG. 9. The brake control strategy will controlactivation of the brake mechanism independently of the release bearingposition, unlike a conventional transmission torque input shaft brake,previously described. The brake control includes a thermal protectiondevice to prevent overheating due to excessive current or excessivebraking.

The electromagnetic brake may operate with a voltage source of 12 to 42volts DC and may be controlled by a remotely placed switch in aconvenient location. The switch may be located, for example, in themaster cylinder of a hydraulic linkage or a clutch pedal linkage or aclutch release mechanism. Upon closure of the switch, which may benormally open, the coil windings for the brake will become energizedthereby creating a magnetic field for braking the armature plate. In thealternative, the remote control switch can be used to activate a controlrelay, which in turn closes a set of normally-open switch contacts. Uponclosure of the normally open switch contacts, power is supplied to theelectromagnetic coil through a circuit protection device.

The circuit protection device, as shown at 154 in FIG. 8, is placed inseries with the coil and will interrupt the current flow path if thecurrent draw exceeds a safe limit or if the temperature build-up in thebrake exceeds predefined temperature limits.

The control system of FIG. 8 includes a vehicle electrical system 134and a brake system controller 136. Control input signals for thecontroller 136 may include signals from a vehicle speed sensor 138, anaccelerator pedal position sensor 139, a transmission reverse sensor140, a brake pedal position sensor 141, a transmission first gear sensor142, a control cylinder position sensor 143, a transmission neutralsensor 144, and a master clutch pedal position sensor for the masterclutch, as shown at 146. These signals are distributed through a controlarea network bus, as shown at 148, to the controller 136. The powersource for the electromagnetic brake may be the vehicle electricalsystem 134. The brake controller 136 ensures that the brake can beactivated only when the engine is running, a fuel solenoid for theengine is energized and an ignition switch is in the key-on position. Itresponds to signals from sensors 146, 152 and 148, 144 and 140 andallows brake engagement only when the master clutch is disengaged andthe vehicle speed is less than a predetermined value “N.” It determineswhether the transmission is in neutral and whether first gear or reversehas been selected.

An alternative control strategy may use inputs from sensors such as, forexample, the accelerator pedal position sensor 139, the brake pedalposition sensor 141, and the control cylinder position sensor 143. Theaccelerator position sensor 139 may be used instead of the engine speedsignal because different engines may be calibrated to idle at differentspeeds. If the accelerator pedal is at least partially depressed, thisindicates that the operator is seeking to accelerate the engine aboveidle which is inconsistent with proper engagement conditions for theinput shaft brake. Since accelerator pedal position, brake pedalposition, and transmission in neutral input signal inputs are notnormally provided on a J1939 bus they may require separate wiring to thesystem controller 136.

The switch that opens or closes the brake circuit is shown at 150. Anover-current protection device, such as a fuse, can be used as shown at152. The circuit protection device 154 may include a thermally activatedswitch that prevents over-heating due to prolonged usage or due to highcurrent.

A control algorithm, seen at FIG. 9, will prevent torque input shaftbrake (clutch-brake) activation when the vehicle engine is off, if thevehicle is moving, or if a preset timer is timed out. The timer preventsthe electromagnetic brake from being abused if the vehicle clutch pedalis held down by the operator for an extended period of time.

In FIG. 9, the strategy will determine at 158 whether the clutch brakeswitch is “on.” If it is not on, the control routine will maintain thebrake in an “off” state, as shown at 160. If the brake switch is on, theroutine determines at decision block 162 whether the engine speed iswithin a high speed limit or a low speed limit.

The engine speed is measured, as indicated at 164. If the engine speedis not within predetermined limits, the routine will maintain the brakein an “off” position, as shown at 160.

If the engine speed is within the high and low limits, a decision ismade at decision block 166 to determine whether the vehicle speed,measured as shown at 168, is less than a precalibrated set point. If thevehicle speed is higher than the set point, the brake will be kept “off”as shown at 160. If the vehicle speed is less than the set point, thebrake is applied, as shown at 170.

When the brake is on, it is determined, as the routine continues,whether the timer is on. This is done at action block 172. If the timeris not timed out, the routine will continue, as shown at 174. If thetimer value is greater than the set point, however, the brake will bekept off as shown at 160.

In FIG. 10, an alternative control algorithm strategy is illustrated.The clutch brake switch 178 may be remotely located anywhere that theoperation of the clutch brake device can be controlled. For example, theswitch 178 can be placed to monitor the position of the master cylinderof the hydraulic linkage, the slave cylinder of the hydraulic linkage,clutch pedal, clutch release mechanism, or the like. The algorithmdetermines at 180 whether the clutch brake switch is “on.” If it is noton, the control routine will maintain the brake in an “off” state, asshown at 182.

If the brake switch is on, the routine determines at decision block 184whether the accelerator pedal is being depressed by the operator. Thismay be expressed in terms of the stroke position of the acceleratorpedal wherein the pedal is not depressed when the pedal position is at0% of its stroke. The accelerator pedal position is detected by a sensorat 186.

The vehicle speed is measured, as indicated at 188. If the engine speedis not within predetermined limits, the routine will maintain the brakein an “off” position, as shown at 182. A decision is made at decisionblock 190 to determine whether the vehicle speed, measured at 188, isless than a precalibrated set point. If the vehicle speed is higher thanthe set point, the brake will be kept “off” as shown at 182. If thevehicle speed is less than the set point, the brake is applied, as shownat 192.

When the brake is on, it is determined, as the routine continues,whether the timer is on. This is done at action block 194. If the timeris not timed out, the routine will continue, as shown at 196. If thetimer value is greater than the set point, however, the brake will bekept off as shown at 182.

Referring to FIG. 11, an electromagnetic clutch brake control isillustrated that includes primary and secondary fall-back engagementcounters. The features described, beginning at the instant in thestrategy operation when the clutch brake switch is operated at 200, thendetermines if the connection to the datalink, such as the J1939 databus,is complete. If a databus fault is not detected at 202, as would beexpected in normal circumstances, the algorithm proceeds to confirm thatthe J1939 based protection limits are active at 204. The brake ON timeris activated at 206. The system determines if the conditions areappropriate for application of the clutch brake. The system determinesat 208 whether the protective inputs from the databus, such as the J1939engine speed, throttle position, vehicle speed timer and the like, arewithin the ranges at 210. If the inputs from the databus are appropriatefor engagement, the system also checks to determine at 208 that thebrake ON timer is enabled. If so, the brake is engaged at 212. Uponbrake engagement, the primary clutch brake counter is incremented at 214and the system returns to “start.” If the conditions are not appropriatefor application of the clutch brake at 208, the system returns to“start” without applying the brake.

If a databus fault is detected at 202, the system then proceeds at 220to set a flag indicating that the J1939 based protection limits aredeactivated. The system is still enabled even without the J1939 basedprotection limits and proceeds at 222 to set the brake ON timer to itsactive state. The system then determines at 224 whether the conditionsare appropriate for application of the clutch brake with reference onlyto the brake ON software timer. If the brake ON timer is appropriate forapplication of the brake, the system proceeds to apply the brake at 226.Following application of the brake at 226, the secondary, or fall-backmode, counter is incremented at 228. The system then returns to “start”for the next cycle. If conditions are not appropriate for application ofthe clutch brake at 224, the system returns to the “start” withoutapplying the brake.

The brake ON timer, referenced at 206 or 222, limits the duration theclutch brake power is applied for a single activation of the clutchbrake switch. Once the timer times out, the clutch brake is turned off.The brake ON timer is set when the clutch brake switch is opened.

The control for the electromagnetic brake described with reference toFIG. 11 provides a protection algorithm that can use any signals thatmay be available from the CAN based J1939 datalink, or the like.However, if the signals are not received from the datalink, theprotection algorithm allows for a fall-back mode of operation for theelectromagnetic clutch brake that allows it to continue to operate evenwithout the inputs from the datalink. The system is permitted to operatebased upon receipt of the input signal from the clutch brake activationswitch. In the fall-back mode, there is less protection for theelectromagnetic brake, which may result in excessive wear due toactivations under conditions that would normally be prohibited by theprotection algorithm.

The number of activations of the brake with the protection algorithmutilizing the input signals from the datalink are counted on the primaryclutch brake counter, at 214. The number of activations of theelectromagnetic clutch brake without data being provided to thealgorithm from the datalink are counted on the secondary, or fall-backmode, counter, at 228.

At service intervals, the counters may be inspected. Upon inspection, itmay be determined whether the clutch brake will operate without thedatalink protection limit at any time during the clutch brake life. Ifso, it may be determined how many activations occur by checking thesecondary, or fall-back mode, counter. This information may be used todiagnose clutch brake wear causes and provide other informationregarding usage and wear of the electromagnetic clutch brake.

Although an embodiment of the invention has been described, it will beapparent to persons skilled in the art that modifications may be madewithout departing from the scope of the invention. All suchmodifications and equivalents thereof are intended to be covered by thefollowing claims.

1. An electromagnetic brake for a vehicle powertrain for a wheeledvehicle, the powertrain comprising an engine, a multiple-ratio powertransmission having a housing enclosing multiple-ratio gear elements, apower output shaft driveably connected to vehicle traction wheels, apower input shaft driveably connected to the multiple-ratio gearelements and a master clutch selectively connecting the power inputshaft to the engine, the master clutch being enclosed by a master clutchhousing forming a part of the transmission housing, the electromagneticbrake comprising: a stator coil housing secured to the transmissionhousing, the stator coil housing enclosing a stator coil surrounding thepower input shaft and defining with the stator coil housing anelectromagnetic pole face; a stator coil circuit including a voltagesource and a switch for opening and closing the stator coil circuit; anarmature plate having a hub portion secured to the power input shaft anda peripheral portion disposed adjacent the stator coil; a control systemfor electrically energizing the stator coil thereby effecting frictionalengagement of the armature plate with the pole face as anelectromagnetic flux flow path is established around the stator coilthrough the stator coil housing and the peripheral armature plateportion; the control system further including a protective circuit thatis adapted to receive at least one data input from a databus, theprotective circuit determining whether the data input is within apredetermined range that is appropriate for energizing the stator coil,and wherein the protective circuit further comprises a fallbackmechanism in communication with the stator coil to permit operation ofthe electromagnetic brake when no data input is received from thedatabus.
 2. An electromagnetic brake according to claim 1 wherein aplurality of data inputs is received from the databus, the data inputscomprises at least one of an engine speed data input, a throttleposition data input, and a vehicle speed timer input.
 3. Theelectromagnetic brake of claim 1 wherein the fallback mechanism in theprotective circuit further comprises a software timer that times theperiod during which the stator coil for the electromagnetic brake isenergized.
 4. The electromagnetic brake of claim 1 wherein fallbackmechanism in the protective circuit further comprises a software timerthat times the duration of electromagnetic brake application to permitoperation of the electromagnetic brake when no data input is receivedfrom the databus.
 5. The electromagnetic brake of claim 1 furthercomprising a primary counter that is incremented each time theelectromagnetic brake is applied as the data inputs are received fromthe databus.
 6. The electromagnetic brake of claim 5 further comprisinga secondary counter that is incremented each time the electromagneticbrake is applied while the data input from the databus is unavailable.7. An electromagnetic brake for a vehicle powertrain for a wheeledvehicle, the powertrain comprising an engine, a multiple-ratio powertransmission having a housing enclosing multiple-ratio gear elements, apower output shaft driveably connected to vehicle traction wheels, apower input shaft driveably connected to the multiple-ratio gearelements and a master clutch selectively connecting the power inputshaft to the engine, the master clutch being enclosed by a master clutchhousing forming a part of the transmission housing, the electromagneticbrake comprising: a stator coil housing secured to the transmissionhousing, the stator coil housing enclosing a stator coil surrounding thepower input shaft and defining with the coil housing an electromagneticpole face; a stator coil circuit including a voltage source and a switchfor opening and closing the stator coil circuit; an armature platehaving a hub portion secured to the power input shaft and a peripheralportion disposed adjacent the stator coil; a control system forelectrically energizing the stator coil thereby effecting frictionalengagement of the armature plate with the pole face as anelectromagnetic flux flow path is established around the stator coilthrough the stator coil housing and the peripheral armature plateportion; the control system further including a protective circuit thatis adapted to receive at least one data input from a databus, theprotective circuit determining whether the data input is within apredetermined range that is appropriate for energizing the stator coilwherein the protective circuit further comprises a software timer thattimes the period during which the stator coil for the electromagneticbrake is energized.
 8. An electromagnetic brake according to claim 7wherein a plurality of data inputs is received from the databus, thedata inputs comprising comprises at least one of an engine speed datainput, a throttle position data input, and a vehicle speed timer input.9. The electromagnetic brake of claim 7 further comprising a primarycounter that is incremented each time the electromagnetic brake isapplied as the data inputs are received from the databus.
 10. Theelectromagnetic brake of claim 9 further comprising a secondary counterthat is incremented each time the brake is applied while the data inputfrom the databus is unavailable.
 11. An electromagnetic brake for avehicle powertrain for a wheeled vehicle, the powertrain comprising anengine, a multiple-ratio power transmission having a housing enclosingmultiple-ratio gear elements, a power output shaft driveably connectedto vehicle traction wheels, a power input shaft driveably connected tothe multiple-ratio gear elements and a master clutch selectivelyconnecting the power input shaft to the engine, the master clutch beingenclosed by a master clutch housing forming a part of the transmissionhousing, the electromagnetic brake comprising: a stator coil housingsecured to the transmission housing, the stator coil housing enclosing astator coil surrounding the power input shaft and defining with the coilhousing an electromagnetic pole face; a stator coil circuit including avoltage source and a switch for opening and closing the stator coilcircuit; an armature plate having a hub portion secured to the powerinput shaft and a peripheral portion disposed adjacent the stator coil;a control system for electrically energizing the stator coil therebyeffecting frictional engagement of the armature plate with the pole faceas an electromagnetic flux flow path is established around the statorcoil through the stator coil housing and the peripheral armature plateportion; the control system further including a protective circuit thatis adapted to receive at least one data input from a databus, theprotective circuit determining whether the data input is within apredetermined range that is appropriate for energizing the stator coil,wherein the protective circuit permits operation of the electromagneticbrake when no data input is received from databus, and wherein theprotective circuit includes a software timer that times the duration ofbrake application.
 12. An electromagnetic brake according to claim 11wherein a plurality of data inputs is received from the databus, thedata inputs comprises at least one of an engine speed data input, athrottle position data input, and a vehicle speed timer input.
 13. Theelectromagnetic brake of claim 11 wherein the protective circuit furthercomprising a primary counter that is incremented each time the brake isapplied as the data inputs are received from the databus.
 14. Theelectromagnetic brake of claim 13 wherein the protective circuit furthercomprise a secondary counter that is incremented each time the brake isapplied while the data input from the databus is unavailable.